Preliminary data are presented which demonstrate the attachment of lymphoma cells to attachment-promoting molecules such as fibronectin and serum spreading factor. Data are also discussed which indicate that normal lymphocytes from the thymus interact with at least one of these molecules--serum spreading factor. It is proposed here to study the interactions of lymphoid cells with known adhesion molecules. A plan is also presented for the identification of novel molecules involved in mediating the attachment of normal lymphocytes. The fact that normal bone marrow cells attach to a monolayer of thymic epithelium indicates that such molecules exist. These molecules will be examined for structure, function, and tissue distribution. The hypothesis is that the selective attachment of immature lymphocytes to molecules within the thymus probably modulates their differentiation, path of migration, and response to external stimuli. Understanding these interactions will give insight into the behavior and development of lymphocytes as well as possibly provide a better understanding of the behavior of lymphoid tumors. New methods which involve the study of cell attachment to electrophoretically separated proteins are proposed for studying this problem. (LB)